[LeetCode] 588. Design In-Memory File System

 

Design a data structure that simulates an in-memory file system.

Implement the FileSystem class:

• FileSystem() Initializes the object of the system.
• List<String> ls(String path)
  • If path is a file path, returns a list that only contains this file's name.
  • If path is a directory path, returns the list of file and directory names in this directory.
  The answer should in lexicographic order.
• void mkdir(String path) Makes a new directory according to the given path. The given directory path does not exist. If the middle directories in the path do not exist, you should create them as well.
• void addContentToFile(String filePath, String content)
  • If filePath does not exist, creates that file containing given content.
  • If filePath already exists, appends the given content to original content.
• String readContentFromFile(String filePath) Returns the content in the file at filePath.

Example 1:

Input
["FileSystem", "ls", "mkdir", "addContentToFile", "ls", "readContentFromFile"]
[[], ["/"], ["/a/b/c"], ["/a/b/c/d", "hello"], ["/"], ["/a/b/c/d"]]
Output
[null, [], null, null, ["a"], "hello"]

Explanation
FileSystem fileSystem = new FileSystem();
fileSystem.ls("/");                         // return []
fileSystem.mkdir("/a/b/c");
fileSystem.addContentToFile("/a/b/c/d", "hello");
fileSystem.ls("/");                         // return ["a"]
fileSystem.readContentFromFile("/a/b/c/d"); // return "hello"

Constraints:

• 1 <= path.length, filePath.length <= 100
• path and filePath are absolute paths which begin with '/' and do not end with '/' except that the path is just "/".
• You can assume that all directory names and file names only contain lowercase letters, and the same names will not exist in the same directory.
• You can assume that all operations will be passed valid parameters, and users will not attempt to retrieve file content or list a directory or file that does not exist.
• 1 <= content.length <= 50
• At most 300 calls will be made to ls, mkdir, addContentToFile, and readContentFromFile.

设计内存文件系统。

Java实现

class FileSystem {
    private class FileNode {
        private TreeMap<String, FileNode> children;
        private StringBuilder file;
        private String name;

        public FileNode(String name) {
            children = new TreeMap<>();
            file = new StringBuilder();
            this.name = name;
        }

        public String getContent() {
            return file.toString();
        }

        public String getName() {
            return name;
        }

        public void addContent(String content) {
            file.append(content);
        }

        public boolean isFile() {
            return file.length() > 0;
        }

        public List<String> getList() {
            List<String> list = new ArrayList<>();
            if (isFile()) {
                list.add(getName());
            } else {
                list.addAll(children.keySet());
            }
            return list;
        }
    }

    private FileNode root;
    
    public FileSystem() {
        root = new FileNode("");
    }
    
    public List<String> ls(String path) {
        return findNode(path).getList();
    }
    
    public void mkdir(String path) {
        findNode(path);
    }
    
    public void addContentToFile(String filePath, String content) {
        findNode(filePath).addContent(content);
    }
    
    public String readContentFromFile(String filePath) {
        return findNode(filePath).getContent();
    }

    private FileNode findNode(String path) {
        String[] files = path.split("/");
        FileNode cur = root;
        for (String file : files) {
            if (file.length() == 0) {
                continue;
            }
            cur.children.putIfAbsent(file, new FileNode(file));
            cur = cur.children.get(file);
            if (cur.isFile()) {
                break;
            }
        }
        return cur;
    }
}

/**
 * Your FileSystem object will be instantiated and called as such:
 * FileSystem obj = new FileSystem();
 * List<String> param_1 = obj.ls(path);
 * obj.mkdir(path);
 * obj.addContentToFile(filePath,content);
 * String param_4 = obj.readContentFromFile(filePath);
 */

 

LeetCode 题目总结